Nowadays, more and more people are using mobile devices for various purposes. A mobile device user may have a plurality of mobile devices for use at the same time. Usually each mobile device has a rechargeable energy reservoir, such as a battery, that obtains energy for storage in the reservoir through a charging device designed specifically for the device or the device's battery. FIG. 1 is a schematic diagram of a device being charged according to the prior art. When a mobile device 100 is in need of charging its battery 130, it is connected, through an inlet connector 110, to a direct current (DC) power source 200. The DC power source may be a power adapter. The adapter has an input end and an output end. The input end is plugged into a regular alternating current (AC) power outlet (100-240V AC). The output end has a galvanic (connector) or non-galvanic (induction field) connection point that is plugged into or coupled with the inlet connector (jack) 110 of the device 100. The DC current from the adapter 200 charges the battery 130 of the mobile device 100. The mobile device typically also contains one or more device circuits 140 that are powered by the battery 130. A conductive connection from the inlet jack 110 to the battery 130 may further contain a controlling element 120 that can disconnect the charging current flow when the battery is full. For many conventional mobile devices, the controlling element 120 is merely a switch. The charging current only flows in one direction, namely from the power source to the device. Commonly, a power adapter is designed for a particular device or for a particular type of battery and for a certain AC voltage. The adapter may not be used for charging a device it is not designed for.
There are problems with the above arrangement. Sometimes a user with a plurality of devices may find that some devices are fully charged and ready to use, others are low on battery level. If the user is traveling, in order to charge all the devices, all the chargers for these devices have to be brought along. The user must make sure that these chargers work properly, because in a remote location the AC outlet might have a different line voltage or a different plug design that would render the chargers unusable. In situations where a device is low on battery and the adapter for charging the device is not available or useable, it is desirable that the device is able to draw energy from an energy reservoir of another device or from a portable energy source such as a battery pack. This means one of the devices should be able to act as a “donor” to provide its stored energy to other devices.
Therefore, what is needed is a method that enables balancing or sharing energy reservoirs between two or more mobile devices. Preferably, an apparatus for performing the method is a simple and compact unit, and may be integrated into a mobile device.